The subject matter disclosed herein relates to an uninterruptible power supply (UPS), and in particular, a UPS input stage that can receive power from different electrical utility configurations.
Uninterruptible Power Supplies are used to provide clean power to critical loads (e.g., protected equipment such as computers, data centers, cash registers) even if the input power source fails. A UPS can provide instantaneous protection from input power source interruptions by supplying energy stored in batteries or other capacitive devices that can power the protected equipment for a sufficient amount of time to start a backup power source or properly shut down the protected equipment. Since critical loads can be found in a variety of residential or commercial locations having different electrical utility configurations (e.g., different alternating current (AC) voltages (120V, 208V, 240V) and/or different number of phases (1 or 2) with different phase angles (120°, 180°, or 240°)). Different UPS's have to be designed for connecting to the different electrical utility configurations.
FIG. 1 is a schematic diagram of an illustrative and exemplary electrical utility configuration 2, having a first voltage source 10 with a first voltage source line (LINE 1) 11, a second voltage source 20 with a second voltage source line (LINE 2) 21, a neutral node (or center tap) 40 with a neutral 41 located between and connecting the first voltage source 10 and the second voltage source 20. The exemplary electrical utility configuration 2 can be representative of a conventional single phase three-wire electrical utility configuration also referred to as a split-phase system or a center-tapped neutral system, since it can be formed by, e.g., center-tapping the secondary winding of a transformer (or generator/alternator) to form a first voltage source 10 and a second voltage source 20. The exemplary service can be representative of two phases of a three-phase four-wire wye electrical utility configuration or two phases of a three-phase three-wire delta electrical utility configuration.
In one example, a first single phase input voltage (V1) between the first voltage source line (LINE 1) 11 and the neutral node 40 is 120VAC at a phase angle of 0°, while the second single phase input voltage (V2) between the second voltage source line (LINE 2) 21 and the neutral node 40 is 120VAC at a phase angle of 180°. Without connecting the neutral 41, the single phase input voltage (V3) between the first voltage source line (LINE 1) 11 and the second voltage source line (LINE 2) 21 is 240VAC. By connecting the neutral 41, a split phase input voltage can be provided with a phase difference of 180° between the two voltage sources 10, 20.
In another example, the first single phase input voltage (V1) between the first voltage source line (LINE 1) 11 and the neutral node 40 is 120VAC at a phase angle of 0°, while the second single phase input voltage (V2) between the second voltage source line (LINE 2) 21 and neutral 40 is 120VAC at a phase angle of 120° or 240°. Without connecting the neutral 41, the single phase input voltage (V3) between the first voltage source line (LINE 1) 11 and the second voltage source line (LINE 2) 21 is 208VAC. By connecting the neutral 41, a split phase input voltage can be provided with a phase difference of 120° or 240° between the two voltage sources 10, 20.
The design of a UPS for a single phase input voltage of 120VAC will be different than the design of a UPS for a single phase input voltage of 208VAC or 240VAC. Similarly, the design of a UPS for a single phase input voltage will be different than the design of a UPS for a split phase input voltage. In addition, since some electrical utility configurations do not have a neutral (e.g., 208VAC or 240VAC single phase) while other electrical utility configurations do have a neutral (e.g., 120VAC single phase), different UPS designs must be provided for these different electrical utility configurations. The requirement for different UPS designs for all of the different possible electrical utility configurations limits the flexibility of the use of the UPS's to protect equipment. For example, a company with locations in areas having different electrical utility configurations would need to purchase and stock a number of different types of UPS to protect its equipment in the different locations where it has operations.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.